The present invention relates to safety devices for open-type combustors, which are employed to extinguish fires in the case of abnormal combustion, for example, room oxygen starvation or the like.
Conventional open-type combustors such as oil stoves or the like when used in a closed room may reduce the oxygen concentration within the room to the point where there is a danger of oxygen starvation. For improving the safety of such open-type combustors, there has been proposed a device for issuing an alarm or extinguishing the fire which includes a control circuit for operating an alarm or a fire-extinguishing device in response to an output from an oxygen starvation sensor mounted on an outer casing provided above a combustion cylinder of the combustor. Such an arrangement is disclosed, for example, in Japanese Unexamined Patent Publication No. 58-99620.
Particularly, as to the fire-extinguishing device, as disclosed in Japanese Unexamined Utility Model Publication No. 50-55239 and Japanese Utility Model Publication No. 56-20707, there has been proposed a fire-extinguishing device employing a thermally deformable element (such as bimetal or the like) which undergoes a displacement upon a thermal difference, the thermally deformable element being mounted in a place (e.g., in the vicinity of an outer-wick-cylinder or the inside of a fire grate) where a change in temperature occurs at times of abnormal combustion conditions, and an aseismatic (antishock, e.g., response to a seismic shock or the like) automatic extinguishing unit operated by an operating frame linked with the aseismatic automatic extinguishing unit and which is actuated by the displacement force of the thermally deformable element in case of abnormal combustion, for example, in case of oxygen starvation.
However, being disposed on the outer casing above the combustion cylinder, such an oxygen starvation sensor cannot completely accurately detect the temperature of the flame in the case of abnormal combustion such as oxygen starvation. There are further problems in that, because the operating frame is disposed in abutment with the thermally deformable element, the responsiveness of the operating frame to temperature changes of the thermally deformable element is poor so that sometimes the aseismatic fire-extinguishing device or the alarm device cannot be properly operated.
On the other hand, in the case of normal fire extinction, when the temperature at the sensor portion provided with the thermally deformable element falls gradually before extinction is complete, passing the temperature corresponding to oxygen starvation, the oxygen starvation unit, constituted by the oxygen starvation sensor, the thermally deformable element, etc., is unavoidably operated, causing the aseismatic automatic fire-extinguishing unit to operate, and thereby extinguishing the fire earlier than would otherwise occur. This results in a problem that malodorous fumes are generated. Similarly, in the alarm unit, there has been a still further problem that, when the oxygen starvation sensor operates when the temperature drops, a switch is turned on to operate the alarm momentarily.
In the case of dry combustion of the wick (namely, burning the wick without oil so as to clean it), the temperature of the sensor portion provided with the thermally deformable element drops gradually, before complete dry combustion in the same manner as in the case of oxygen starvation, thereby operating the oxygen starvation unit, resulting in another problem that complete dry combustion of the wick cannot be performed. In the alarm unit, there is also a difficulty in that the oxygen starvation alarm may light or sound as the temperature drops.
Moreover, in the case of dry combustion of the wick, there has been a yet further problem that if a dry combustion lock knob locking the oxygen starvation sensor unit is not released properly, the oxygen starvation sensor unit cannot operate in the case of oxygen starvation, nor can the aseismatic automatic fire-extinguishing unit.